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ObjectiveDeclining participation has been observed in previous epidemiological studies, could occupational risk factor epidemiology be particularly vulnerable to this trend? The objective of this study was to assess trends of participation rates in occupational case-control studies.MethodsFive prominent occupational and epidemiological journals were pre-selected and all articles published between 1991 and 2017 were screened for case-control studies of occupational risk factors for chronic disease outcomes. The primary independent variable was median year of data collection, while the primary outcome variable was reported participation rate. We conducted linear regression, adjusting for study characteristics that included study gender mix, location of recruitment, disease outcome, and data collection method.ResultsA total of 180 studies published in the five journals were included in the final analysis. The mean participation was higher for cases (78.9%) than for controls (71.5%). In linear regression, a significant trend of decreasing participation was observed for both cases with a percent change of −0.50 per year (95% CI −0.75 to −0.25) for cases and a percent change of −0.95 per year (95% CI −1.23 to −0.67) for controls. After adjustment for study gender mix, location, disease outcome, and data collection method, the trend remained statistically significant for both case and control groups.ConclusionDeclining participation rates in case-control studies of occupational risk factors may reflect an overall decline of participation in population-based samples. Lower participation rates introduce the potential for bias and may deter future population-based studies of occupational risk factors.

Background Head injury is a hypothesised risk factor for Parkinson9s disease, but there is a knowledge gap concerning the potential effect of injury circumstances (eg, work-related injuries) on risk. The objective of this study is to address this gap while addressing issues of recall bias and potential for reverse causation by prediagnosis symptoms. Methods We conducted a population based case-control study of Parkinson9s disease in British Columbia, Canada (403 cases, 405 controls). Interviews queried injury history; whether injuries occurred at work, in a motor vehicle accident or during sports. Participants were also asked to report their suspicions about the causes of Parkinson9s disease to provide an indicator of potential recall bias. Associations were estimated with logistic regression, adjusted for age, sex and smoking history. Results Associations were strongest for injuries involving concussion (OR: 2.08, 95% CI 1.30 to 3.33) and unconsciousness (OR: 2.64, 95% CI 1.39 to 5.03). Effects remained for injuries that occurred long before diagnosis and after adjustment for suspicion of head injury as a cause of Parkinson9s disease. Injuries that occurred at work were consistently associated with stronger ORs, although small numbers meant that estimates were not statistically significant. Conclusions This study adds to the body of literature suggesting a link between head injury and Parkinson9s disease and indicates further scrutiny of workplace incurred head injuries is warranted.

Objectives Mining workers in Canada may be exposed to several potential carcinogens including crystalline silica, various metals, and diesel exhaust. This study aimed to assess the risk of cancer among male mining workers employed in various Canadian mining sectors. Method The Cohort was created by Statistics Canada through the linkage of the 1991 Canadian Census (long form) to the Canadian Mortality Database, Canadian Cancer Registry, and annual Tax Summary Files (1991–2006). This linkage resulted in a cohort of 1.1 million working males aged 25–74, including over 14 000 workers employed in the mining industry. Cox proportional hazards modelling was used to estimate hazard ratios (HR) and corresponding 95% confidence intervals, adjusted for age and region. Results There were 700 cancers among 660 mining industry workers. There was an increased risk for rectal cancer (HR: 1.37, 1.01–1.88), particularly in gold mining (HR: 3.11, 1.47–6.56). Increased risks of kidney and prostate cancer were observed for coal mining (HR: 2.71, 1.12–6.57 and HR: 1.80, 1.10–2.94, respectively), and esophageal cancer in metal mining other than gold or iron (HR: 2.78, 1.13–6.80). There were also elevated risks for stomach and laryngeal cancer among mining workers. Conclusions This study identified increased risks of rectal, kidney, prostate, and esophageal cancers among male mining industry workers employed in specific sectors. There are also a number of limitations and challenges that accompany the investigation. Our findings may have important implications for our understanding of occupational cancer risk factors and potential policy interventions in the mining industry.